If you’re a nonprofit, getting your message out to supporters is your most important lifeline when you’re looking for volunteers or donations. So nonprofit managers have spent the last decade composing Facebook posts, tweets, LinkedIn missives, and e-mail blasts to keep their cause top of mind.

But all those tweets and posts may be getting lost in a sea of chatter, said Greg McHale, the founder of BiddingForGood, the Cambridge-based charitable auction site. E-mail open rates and response rates were down in 2015, according to a M+R Benchmarks study, which evaluates the effectiveness of online messaging efforts made by nonprofits.

“Part of the reason it’s declining is that we’re looking at e-mails on smartphones,’’ McHale said, noting that the fleeting way we scan them on the go means people rarely pause to act. So if charities want to reach their markets, they need to get in front of supporters with an immediate call for action. To McHale that means the home screens of their smartphones.

On Monday, McHale unveiled his new app, LetsAllDoGood, which is designed to allow nonprofits to send push notifications to their supporters. The app features a number of participating organizations, and users can choose to receive updates from the ones they care most about.

So if the United Way of Boston needs volunteers for a walk-a-thon, it can try and recruit them with a simple ping. Or if the Medfield Animal Shelter is having a puppy adoption day, it can push out a reminder that their supporters will see instantly on their phones.

The app is launching with10 Boston-area nonprofits, including Zoo New England, Boston Partners in Education, and the Foundation for MetroWest, and McHale said he plans to bring on 20 more organizations soon. He hopes to eventually open the platform to any nonprofit or charitable effort, from the million-dollar fund-raising powerhouse to the local PTA.

The business model, he said, is driven in part by the corporate sponsors who are underwriting many of these nonprofits to begin with. The organizations can either have the sponsor opt to pay $99 a year fee to have their branding embedded within the app, or the organization can pay $75 and offer it as a benefit for their corporate supporters.

Mark Lamothe, the marketing director of the United Way of Mass Bay, said he’s hoping the app will provide the organization with an opportunity for direct, yet unobtrusive, connections with his supporter base. He said he’s felt the squeeze as platforms such as Twitter and Facebook are increasingly relying on algorithms to give their users the content they find most interesting.

“If you’re connected to United Way on Facebook but you’re not liking or interacting with our posts, the algorithms are going to make them less important on your feed,’’ he said.

LetsAllDoGood allows him to bypass that loophole and get directly into the place in the information stream that we’re almost hard-wired to respond.

“In a world where you just seem to be bombarded by information, it seemed to be a smaller space and a more focused space,’’ he said.

The fact that the push notifications were opt-in is key, he added. “It’s not viewed as spam because it’s something you chose to want to hear about.’’

Janelle Nanos can be reached at janelle.nanos@globe.com. Follow her on Twitter @janellenanos.